An FeII Spin‐Crossover Complex Becomes Increasingly Cooperative with Ageing. Issue 5 (21st November 2012)

• Record Type: Journal Article
• Authors: Craig, Gavin A.; Costa, José Sánchez; Roubeau, Olivier; Teat, Simon J.; Aromí, Guillem
• Other Names: Murray Keith S. sponsoringEditor.; Oshio Hiroki sponsoringEditor.; Real Jose Antonio sponsoringEditor.
• Is Part Of: European journal of inorganic chemistry. Issue 5/6(2013)
• Page Start: 745
• Page End: 752
• Publication Date: 2012-11-21
• Subjects: Spin crossover -- Iron -- Magnetic properties -- Intermolecular interactions -- Hirshfeld surfaces; Chemistry, Inorganic -- Periodicals; Organometallic chemistry -- Periodicals; Bioinorganic chemistry -- Periodicals; Solid state chemistry -- Periodicals; 546
• DOI: 10.1002/ejic.201201041
• Languages: English
• ISSNs: 1434-1948

Abstract

Abstract: The polypyrazolyl ligand H4 L, a functionalised derivative of 3‐bpp [bpp = bis(pyrazol‐3‐yl)pyridine], has been used to synthesise an Fe II spin‐crossover (SCO) system [Fe(H4 L)2 ](ClO4 )2 · 2THF· H2 O (1 ). A subsequent magnetic and structural study revealed that the compound undergoes an incomplete transition with a small hysteresis loop of 8 K and a large residual high spin (HS) fraction. This is consistent with single crystal diffraction results at 250 and 90 K, which show a slight modification of the crystal packing and Fe–N bond lengths. Ageing of the samples leads to more cooperative SCO behaviour, as evidenced by a concomitant increase in the width of the hysteresis loops (reaching up to 20 K) and a decrease in the residual HS fraction at low temperatures. These increases in the bistable domain of the sample, corroborated by measuring the changes in heat capacity through differential scanning calorimetry, are accompanied by a loss of crystallinity, which is attributed to solvent loss and the absorption of atmospheric water. Grinding an aged sample yields a narrower hysteresis loop at higher temperatures. Compound1 was compared with two previously observed systems of the same family that exhibit different SCO behaviour, [Fe(H4 L)2 ](ClO4 )2 · H2 O· 2(CH3 )2 CO (2 ) and [Fe(H4 L)2 ](ClO4 )2 · 2C3 H7 OH (3 ), by using Hirshfeld surface analysis to have a global view of the intermolecular interactions as enhanced by the functional groups of H4 L. Abstract : Improving with ageing! A bpp‐type [bpp = bis(pyrazol‐3‐yl)pyridine)] ligand, H4 L, designed to enhance intermolecular interactions, leads to the spin‐crossover (SCO) compound [Fe(H4 L)2 ](ClO4 )2 · 2THF· H2 O, which exhibits enhanced spin transition cooperativity with ageing. The intermolecular interactions as a whole are analysed and compared with those of related compounds by the use of Hirshfeld diagrams.